Graphene is a remarkable material, a monolayer of carbon atoms bonded together in a honeycomb structure that exhibits extraordinary electronic and optoelectronic properties; such as a zero band gap energy, high electron mobility and ultrahigh mechanical strength. The electronic properties of graphene can lead to nonlinear optical processes such as high harmonic generation. Here, we investigate high harmonic generation in several graphene configurations. We first report on the observation of harmonic generation in monolayer graphene on a quartz substrate. We measured up to the ninth harmonic (233 nm wavelength) from graphene of a mid-infrared femtosecond laser, whose wavelength is 2.1 µm, pulse energy around 6 nJ, pulse duration 85 fs, and repetition rate 18 MHz. Our findings confirm recent observations . We then report for the first time on the observation of harmonics from free-standing graphene supported on TEM grids. Free-standing graphene, in contrast to graphene on a substrate behaves differently; mainly due to the lack of its interaction with the substrate which alters its band gap. We will present major trends of high harmonic generation dependence with laser polarization, intensity and a study on damages issues .
 Yoshikawa et al., Science 356, 736_738 (2017)
 Nicolas et al. submitted.
Nanoscale amplification of non-linear processes in solid-state devices opens novel applications in nano-electronics, nano-medicine or high energy conversion for example. Coupling few nano-joules laser energy at a nanometer scale for strong field physics is demonstrated. We report enhancement of high harmonic generation in nano-structured semiconductors using nanoscale amplification of a mid-infrared laser in the sample rather than using large laser amplifier systems. Field amplification is achieved through light confinement in nano-structured semiconductor 3D waveguides. The high harmonic nano-converter consists of an array of zinc-oxide nanocones. They exhibit a large amplification volume, 6 orders of magnitude larger than previously reported  and avoid melting observed in metallic plasmonic structures. The amplification of high harmonics is observed by coupling only 5-10 nano-joules of a 3.2 µm high repetition-rate OPCPA laser at the entrance of each nanocone. Harmonic amplification (factor 30) depends on the laser energy input, wavelength and nanocone geometry .
 Vampa et al., Nat. Phys. 13, 659–662 (2017).
 Franz et al., arXiv:1709.09153 [physics.optics] (2017)